Protection of the environment is a topic of fundamental importance of mankind. Various factors contribute to pollute the environment, which has become a major concern on a global scale. Developed countries and the developing ones have come together to establish national programs to fight against the various source of pollution. The climate perturbations caused by the greenhouse effect, the depletion of the ozone layer, acid rain are the effects of global pollution.
Natural gasses are considered to be one of the most clean and ecological energy for the future and it is considered to be one area of competitiveness for the various oil companies. In recent years dry reforming of methane has become one of the most commonly used process to produce high value added products using two greenhouse gases. Global demand for cleaner energy is increasing and clean hydrogen in the proton exchange membrane fuel cell, ultraclean gas-to-liquid (GTL) fuels are of great interest as an alternative source of energy now. Methane is the least reactive and most abandoned natural gas. So, selective oxidative functionalization of methane is of great importance due to the growing energy demand and the depletion of fossil fuel.
Methane may also contain some impurities like ethane, propane, and other gasses like hydrogen sulfide, carbon dioxide, nitrogen etc. the use of natural gas as a feedstock to produce other valuable chemicals is uneconomical because of the costly storage process and the transportation system available at the areas where natural gasses are mostly available. Particularly in recent years many methods has been investigated to produce more valuable products or easily transportable fuels. But the yields are found to be too low and some of them are much more reactive than methane itself. Therefore the produced chemicals are unable to compete with the oil. At this point of time the most useful way to use methane to produce other valuable chemicals is through an intermediate known as synthesis gas. Nowadays several synthesis gas production processes are available according to industrial application. Syngas can be produced by steam reforming of methane, dry reforming of methane, partial oxidation of methane or decomposition of methanol (mainly used in the hydrogen production for the fuel cell because methanol is high in energy density and is also easy to transport).
Dry reforming is one of the process in which synthesis gas is produced with extremely high selectivity. It was first studied by Fischer and Tropsch. They reported that all the gr. (VIII) transition metals are capable of producing synthesis gas by dry reforming. Ni is capable of showing good results for the dry reforming. But the problem with Ni is the rapid deactivation of the catalyst due to sintering and coking of the catalyst. Noble metals like Rh, Ru, Pd, Pt and Ir catalysts are capable of dry reforming with low carbon formation thus less deactivation of the catalyst. But from the industrial point of view it is more preferable to develop a non-noble metal based catalyst to avoid high cost and less availability of the noble metals. Ni based catalyst has drawn very much attraction for the purpose because of its high reactivity and wide availability. There are reports on dry reforming of methane over different solid catalyst but to the best of our knowledge there is no reference for the use of Ni—MgO—ZnO catalyst for this purpose.
Reference may be made to article in the Catalysis Today, 2011, 171, 132-139 by I. Sarusi et. al. where they reported about 15% methane conversion with CO/H2 ration of ≥2 at 500° C. over doped Rh/Al2O3 catalyst.
Reference can be made to the article in Green Chemistry, 2003, 5, 209-212, where A. Auroux et. al. reported about 70% methane conversion at 600° C. over Co—MgO/SiO2 catalyst with feed ratio CH4:CO2:He=2:1:7 but the catalyst stability is about 24 hrs.
Reference can be made to the article in Green Chem., 2007, 9, 577-581, where Susan M. Stagg-Williams et. al. reported 28% conversion of methane at 800° C. over 0.5% Pt—ZrO2 catalyst with CH4:CO2 feed ratio 1:1 comprising of 80% of the feed using O2 permeable ceramic membrane for the CO2 reforming of methane to syngas. The meanwhile it is been observed that the membrane reactor which catalyses the reaction itself get deactivated (50%) after 14 h.
Reference can be made to the article in Catalysis Letters 70 (2000) 117-122, where Malcolm L. H. Green et. al. reported Mo2C catalysts supported on SiO2 and Al2O3 with over 90% methane and over 85% CO2 conversion and H2/CO ratio over 0.95 at 947° C., and 8 bar pressure.
Reference may be made to article in the Catalysis Communication, 2001, 2, 255-260, in which Aika et. al reported the use Ru supported TiO2 catalyst for dry reforming of methane. At industrial condition, at 0.1 MPa and 800° C. the catalyst shows a stable activity for 25 h time on stream with CO2 conversion of ˜46%.
Reference may be made to US patent no US2007/0253886A by Abatzoglou and his group. Where they used active metal (mainly Ni) deposited on non-porous metallic and ceramic support; the catalyst shows very high methane conversion of 98% at 800° C. with H2/CO ratio of 0.98. But the catalyst stability was limited up to 18 h time on stream.
Reference may be made to article in the Chemical Communication, 2001, 415-416 in which Japanese worker Fujimoto and his group reported the production of syngas by pulse irradiation technique on a mixture of CH4 and CO2 at low temperature and atmospheric pressure. They achieved almost 42% methane conversion with H2/CO ratio of 1.5 with 1:1.5 CH4 to CO2 feed ratio at 180° C. while in presence of Ni—MgO catalyst the same technique gives almost 69% methane conversion while the H2/CO ration goes down to 0.86 with 1:1 CH4 to CO2 feed ratio.
Reference may also be made to article in the ACS Catalysis, 2012, 2, 1331-1342, in which Chou et al. reported a mesoporous tri-metallic composite of NiO—CaO—Al2O3 in the dry reforming of methane. In this report they found 89% of methane conversion at 750° C. whereas the GHSV is 15000 ml g-1 h-1. But the H2/CO ratio is only able to rise up to 0.88 at 750° C.
Reference may be made to article in the Chem. Cat. Chem. 2011, 3, 593-606, where Glaser et. al. reported a highly stable and porous zirconia as support. With 5% Ni supported on ZrO2 they achieved 75% methane conversion at 750° C. with a comparatively slow GHSV of 7.2×104 ml h−1 g−1.
All the above prior art indicates a process exhibit sufficiently high conversion and high selectivity of synthesis gas with H2/CO ratio 1, the main drawback of the processes so far reported is the rapid deactivation of the catalyst.
References were also made be to journal Naeem Awais Muhammad et. al. 2013. International Journal of Chemical Engineering and Applications. Vol. 4(5):315-320), which discuss a polyol process for the production of Nano supported (CeO2, ZrO2 and Al2O)3, Ni catalysts and reforming of methane over such catalysts.
The process in the prior art is different with respect to the use of the Ni—ZnO—MgO catalyst in the present invention which remains activated during reforming of methane upto 100 hrs.
References were also made be to journal Kyoung Soo Jung et al. 1999. Bull. Korean Chem. Soc. Vol. 20(1):89-93, which discloses a fact that the nickel catalysts supported on ZnO and MgO between pH 5 and pH 13 exhibits the enhancement in the activity of reforming of Methane.
The present invention is different from the prior art citation as it discloses a novel process production of Ni—ZnO—MgO which is then used for reforming of methane.
The following are the drawbacks of the hitherto prior art citations which have been addressed in the present invention:                1. Rapid deactivation of the catalyst during reforming of methane,        2. conversion of methane and CO2 to synthesis gas but all the cases the conversion is low at the same time the selectivity is also very low,        
To overcome this problem many researchers used noble metals like Pt, Ru, Rh, Pd etc. which leads to another boundation the high cost and relatively poor availability of these metals. In this kind of situation Ni based catalyst are considered to be most fruitful. There is, therefore, an evident necessity for further improvements in the Ni based catalyst and process for the dry reforming of methane with carbon dioxide.
Our present invention of Ni—MgO—ZnO catalyst will have the possibility to produce synthesis gas from methane and CO2 with very high selectivity at the same time it will produce synthesis gas with H2 to CO mole ratio of around 1, which can be used for the synthesis of chemicals and also can be directly use for the Fischer-Tropsch synthesis.